In one conventional type of fluid treatment known as dead end treatment, a fluid to be treated is introduced into a fluid treatment element, and the entirety or substantially all of the fluid is passed through a fluid treatment medium of the fluid treatment element to be filtered or otherwise treated. In another conventional type of fluid treatment known as crossflow filtration, a fluid to be treated is introduced into a fluid treatment element and is made to flow along the surface of a fluid treatment medium of the fluid treatment element. This flow of fluid along the surface is usually referred to as crossflow. Only a portion of the fluid passes through the fluid treatment medium to be filtered or otherwise treated, while the remainder of the fluid is discharged from the fluid treatment element without passing through the fluid treatment medium.
The fluid which is introduced into the element for treatment is usually referred to as process fluid, the fluid which passes through the fluid treatment medium is usually referred to as permeate, while the fluid which is discharged from the fluid treatment element without passing the fluid treatment medium is usually referred to as retentate. The crossflow of fluid along the surface of the fluid treatment medium generates a fluid shear force in the fluid adjoining the fluid treatment medium which slows the rate at which particles accumulate on the fluid treatment medium.
Each of these types of fluid treatment methods has advantages and disadvantages. In certain crossflow treatment or filtration, since particles accumulate on the surface of a fluid treatment medium more slowly than in dead end treatment, a fluid treatment element operated in a crossflow mode will typically have a longer useful life before requiring cleaning or replacement than a fluid treatment operated in the dead end mode. On the other hand, a fluid treatment element operated in crossflow mode requires greater volumes of fluid than does a fluid treatment element operated in dead end mode, since much of the fluid introduced into the fluid treatment element exits from it as retentate.
Furthermore, a crossflow fluid treatment element may require higher flow velocities than a dead end fluid treatment element, since a certain crossflow velocity is necessary to produce an adequate fluid shear force to prevent the accumulation of particles on the fluid treatment medium. For these reasons, a fluid treatment system employing a crossflow fluid treatment element is usually more complicated than one employing a dead end fluid treatment element and may be unsuitable for situations in which it is desired to treat small volumes of fluid at low flow rates.
The foregoing shows that there exists a need for a fluid treatment element that is capable of providing the advantages of crossflow as well as dead end treatment modes. There further exists a need for a method of cleaning fluid treatment elements such as filter elements which become loaded with particles during fluid treatment.
Furthermore, in the treatment of fluids, for example, in the dissolution of or removal of gases in liquids, certain problems are encountered. For example, in a conventional method of dissolving gases such as by bubbling a gas into a liquid, the resulting solution contains tiny gas bubbles. Such solutions are unfit for certain applications that require stringent purity, for example, in the manufacturing of semiconductors. The fluids considered for cleaning of the silicon wafer, particularly corrosive or active fluids such as ozonated water, ozonated sulfuric acid, or aqueous solutions of hydrofluoric acid, when prepared by conventional methods contain bubbles that may adhere to the wafer and adversely affecting the quality or performance of the semiconductor. Further, such conventional methods, as they operate on a sparging mode, provide rather low or inefficient gas to liquid transfer or dissolution rates.
Thus, there exists a need for a system or arrangement for treatment of fluids, for example, dissolution of or removal of gases in liquids. There further exists a need for fluid treatment elements which are resistant to corrosive fluids. There further exists a need for fluid treatment elements that do not degrade or release contaminants into the process fluids. Thus, there exists a need for fluid treatment elements that are free or substantially free of extractables.
These and other advantages of the present invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.